Sir Scotty I'm driving a 24 year old car. It's only got 93 000 miles, but my dad changed the oil every 6000 miles with 15w40 conventional oil. I've been using it for a year and a half now and I change the oil every 3000 miles. It doesnt't burn that much oil, probably a quart per 3000 miles. Do you think I should switch to a heavier oil and if yes, how heavy? I wanna keep the car for a long time